The catch: Only one ticket, good for two free entries, is allowed per household, but because the ticket application is web-based, this rule is easy to sidestep. Tickets cannot be reused, so choose your museum and your group size accordingly.

To avoid paper waste, some museums will accept an image of the ticket on your smartphone. Check your museum's information page on the Museum Day site to find out whether it participates in paperless ticketing. The information pages also provide details on museum hours and current exhibits.